Marin Master Gardeners: Is that really a geranium?

When is a geranium not a geranium? When it's a pelargonium! And that's much more often than you think. The stalwarts of the summer patio, those brilliantly colored, lollipop shaped blooms spilling over the edges of containers are not, in fact, geraniums, they're pelargoniums. So what's the difference?

True geraniums, also known as cranesbills, are hardy perennials that generally die down in the fall and reappear in the spring. Most are low growing, spreading plants that work wonderfully as groundcovers. They tolerate shade and have delicate looking foliage and blooms in shades of white, pink, lavender and blue.

There are upright and trailing forms, plants with intricately marked and scented foliage, and something for just about any gardener's taste.

Plants that gardeners have been calling geraniums for hundreds of years are members of the Geraniaceae family, as are true geraniums. The confusion with the names arose when pelargonium plants, native to South Africa, were introduced into Europe. These new exciting plants were labeled by nurseries as geraniums until some observant botanists noted differences in the imported plants and went instead with the botanical name of pelargoniums. Nurseries were loath to change, so the common name of geranium persisted.

Pelargoniums are woody or shrubby perennial plants that bloom spring through fall. They sport clusters of flowers with five petals shaped like saucers, stars, butterflies, trumpets or funnels, in eye-popping colors that you can see a block away. There are upright and trailing forms, plants with intricately marked and scented foliage, and something for just about any gardener's taste.

The most common type of pelargonium is the zonal, adorned with large, globe-shaped flowers of fire-engine red, florescent orange, soft peach, salmon and creamy white. Their fancy leaves are marked by distinct bands — or zones — of darker pigments, tri-colored leaves or leaves with silver or white markings.

Blooms of the regal pelargoniums, often referred to as "Martha Washington geraniums," have spectacular showy flowers reminiscent of azalea blossoms. Sometimes, at the peak of the summer season, the dark-green, crinkled leaves are almost invisible, completely smothered with blossoms. Flower colors range from pale to vivid shades of white, purple, pink, red and maroon, often in captivating combinations.

The vine-like growth habit of ivy geraniums make them a favorite for window boxes and hanging baskets. Smooth, leathery, succulent leaves frame jewel-tone blooms with narrow petals and less dense flower heads than zonals.

Grown primarily for their foliage, the soft, finely textured leaves of scented pelargoniums have intriguing shapes and coloration along with pungent fragrances of rose, nutmeg, apple, peppermint and lemon. Leaves can be used for making potpourris, sachets and tea flavorings, and can often be grown as houseplants.

Pelargoniums thrive in light and loamy well-drained soil that receive six to eight hours of sun each day; in hot climates, they enjoy some mid-day shade. Protect them from cold; most will not survive temperatures below freezing. Water regularly, but do not over-water. Nothing can kill this plant quicker than soggy soil due to poor drainage. Deadhead faded flowers regularly to stimulate repeat blooming.

If you're growing plants in containers, apply a balanced fertilizer after new growth appears and repeat the application every few weeks throughout the growing season per product label directions. If you're plants are growing in rich garden soil, they generally don't need any additional plant food.

The most common pests of pelargoniums are aphids, whiteflies, mealybugs and spider mites. All of these insects suck nutrients from the plants and excrete excess sugar that in turn provides a source of food for black sooty mold. Spraying the insects with a dilute soap solution can often be all that is needed to wipe out the pests. Mealybugs can be a little trickier as they are covered by a cottony mass and often live where the stem and leaf join. Use a cotton swab dipped in alcohol to knock them out.

The University of California Marin Master Gardeners are sponsored by UC Cooperative Extension. For questions about gardening, plant pests or diseases, call 473-4204 from 9 a.m. to noon, and 1 to 4 p.m. weekdays, or bring in samples or pictures to 1682 Novato Blvd., Suite 150B, Novato.